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1. Case studies and archaeological feedback

Combined GPR and Electrostatic Prospection in the Roman Colony of Vienna (France)

Christophe Benech, Benjamin Clément, Michel Dabas, Lionel Darras, Lionel Flageul, Côme Parfant, Lola Perruchon-Monge, Cyril Schamper, Alain Tabbagh et Quentin Vitale
p. 27-30

Résumé

– Electrical resistivity and dielectric permittivity mapping using an electrostatic survey device.

– GPR delineation of probable ancient anchor point of the ancient bridge.

– Combination of GPR and electrostatic surveys for urban archaeology.

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Texte intégral

The site

1The Roman colony of Vienna is located at the site of the current city of Vienne (Isère), on the left bank of the river Rhône, at its confluence with the Gère tributary river. It was probably founded by Emperor Octavian between 40 and 27 BC. From the Augustan period, the distinctive features of Roman town planning made their appearance and developed (forum, temple of Rome and Augustus, basilica, theater, rampart) along with a road network, which overlaid partially the axes of the Gallic village. It was also at this time that the suburban district of Saint-Romain-en-Gal was set up, along a wide road coming from Lyon. Under the reign of Claudius, the town planning seems to experience a new growth, which could be partly linked to the consequences of an earthquake that struck the city under Caligula (Adjadj et al., 2014: 119-128). It was at this time that the outskirts of the city reached their final extension while the road network was definitively defined.

2The geophysical surveys carried out throughout the suburban area of ancient Vienne concerned four sectors: the so-called “Palais du Miroir”, probably former thermal baths of Saint-Romain-en-Gal; the district of Sainte-Colombe where excavations, carried out in 2017, allowed the exploration of an entire district located at the outlet of the southern bridge (Clément, 2019); the right bank of the river Rhône for looking at the location of the bridge which allowed the crossing of the river, and finally the southern district of Vienne, which included a circus and a warehouse area.

Methods

3These surveys were carried out using electrostatic and ground-penetrating radar methods. The electrostatic method can be presented as a generalization of the electrical method (Grard & Tabbagh, 1991) where four electrostatic poles, placed in contact with the ground, are used to inject the current and to measure the resulting potential difference. Therefore, the electrical resistivity and the dielectric permittivity (polarization capacity) can be estimated without needing to plant electrodes in the ground, when the latter has a value high enough. As it is the case for the electrical method, its sensitivity to pipe and cable utilities is very low, which is very advantageous in complex urban contexts.

4The two electrostatic devices which were used during the prospecting in Vienne are:

  • The “sliding carpet” (Fig. 1a) which above all makes it possible to carry out profiles (or sliding sounding) in the streets with an investigation depth of up to 3 to 4 m (less if the most superficial layers are electrically conductive). The current version was recently used in Larnaca (Cyprus) to locate the old rampart of the town of Kition (Benech et al., 2017), and in Sweden to identify areas of low electrical resistivity indicating potential areas of strong corrosion (salt infiltration) of the district heating network (Rejkjær et al., 2020).

  • The “MP3” (Fig. 1b) which is primarily designed to perform mapping with a maximum investigation depth of around 2 m. The current version (Flageul et al., 2013) was recently used for archaeological purposes on the Grande Place in Brussels (Blary et al., 2018), together with ground penetrating radar measurements.

5The ground penetrating radar device used in the field is a Stream X multi-antenna from IDS GeoRadar (Fig. 1c). It consists of an array of 8 antennas, operating at a center frequency of 200 MHz and spaced 12 cm apart. This configuration allows high-resolution recording of the amplitude of reflection of electromagnetic waves in the ground over a width of 72 cm in one pass.

6The surveys consisted of a series of profiles in the streets intersecting the sought-after structures (streets, circus, basement of the bridge, building foundations). Only the sectors of Sainte-Colombe and the “Palais du Miroir” could be the subject of more extensive exploration by mapping.

Figure 1. Geophysical devices used during the survey: a) Electrostatic “sliding carpet”, b) Electrostatic MP3, c) IDS Georadar (Stream X V8).

Figure 1. Geophysical devices used during the survey: a) Electrostatic “sliding carpet”, b) Electrostatic MP3, c) IDS Georadar (Stream X V8).

Results

7The surveys carried out in July 2020 were a first exploratory step in the use of geophysical methods for the study of ancient topography in the municipalities of Vienne, Sainte-Colombe and Saint-Romain-en-Gal. The objective of this preliminary study was to estimate the performance of the two geophysical methods, mainly used in modern urban settings, namely the electrostatic method and the ground penetrating radar method, according to the environmental and archaeological context of the different sectors.

8It was in the southern sector of the ancient city of Vienne that the most interesting results were obtained: geophysical exploration made it possible to identify several streets and specify the location of the circus. On the quays of the right bank, the profiles produced have identified a sector that could be the anchor point of the ancient bridge (Fig. 2), in agreement with other archaeological evidence.

Figure 2. Profiling along the Saint-Colombe quay: a) Apparent resistivities from the first two channels of the electrostatic carpet device (forward and backward), b) GPR time slice.

Figure 2. Profiling along the Saint-Colombe quay: a) Apparent resistivities from the first two channels of the electrostatic carpet device (forward and backward), b) GPR time slice.
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Bibliographie

Adjadj, F., 2013. Vienne, 38/2, Carte archéologique de la Gaule, Académie des Inscriptions et Belles-Lettres, 555 p.

Benech, C., Audebert, M., Chevalier, A., Darras, L., Flageul, S., Fourrier, S., Rabot, A., Rejiba, F., Schamper, C., Tabbagh, A., 2017. Revealing the topography of the Ancient Kition (Larnaka, Cyprus): an integrated approach, 12th International Conference of Archaeological Prospection (University of Bradford, UK, 12-16 September).

Blary, F., Sosnowska, P., Charruadas, P., Van Nieuwenhove, B., Dabas, M., Flageul, S., Tabbagh, A., 2018. Prospection de la « grand place » de Bruxelles : utilisation de la méthode électrostatique, 11e colloque GEOFCAN (Antony, France, 20-21 novembre).

Clément, B., 2020. Un quartier antique de la colonie romaine de Vienne figé par les flammes. Premiers résultats des fouilles du Bourg à Sainte-Colombe, Bulletin de la SFAC, XLX, 2018-2019, Revue Archéologique, 69(1), 185-191.

Flageul, S., Dabas, M., Thiesson, J., Rejiba, F., Tabbagh, A., 2013. First in situ tests of a new electrostatic resistivity meter, Near Surface Geophysics, 11(3), 265-274.

Grard, R., Tabbagh, A., 1991. A mobile four electrode array and its application to the electrical survey of planetary ground at shallow depths, Journal of Geophysical Research, 96, 4117-4123.

Rejkjær, S., Finco, C., Schamper, C., Rejiba, F., Tabbagh, A., König, J., Dahlin, T., 2021. Determination of the resistivity distribution along underground pipes in urban contexts using galvanic and capacitive methods, Near Surface Geophysics, 19, 27-41.

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Table des illustrations

Titre Figure 1. Geophysical devices used during the survey: a) Electrostatic “sliding carpet”, b) Electrostatic MP3, c) IDS Georadar (Stream X V8).
URL http://journals.openedition.org/archeosciences/docannexe/image/8180/img-1.jpg
Fichier image/jpeg, 1,4M
URL http://journals.openedition.org/archeosciences/docannexe/image/8180/img-2.jpg
Fichier image/jpeg, 947k
URL http://journals.openedition.org/archeosciences/docannexe/image/8180/img-3.jpg
Fichier image/jpeg, 4,3M
Titre Figure 2. Profiling along the Saint-Colombe quay: a) Apparent resistivities from the first two channels of the electrostatic carpet device (forward and backward), b) GPR time slice.
URL http://journals.openedition.org/archeosciences/docannexe/image/8180/img-4.jpg
Fichier image/jpeg, 473k
URL http://journals.openedition.org/archeosciences/docannexe/image/8180/img-5.jpg
Fichier image/jpeg, 3,0M
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Référence papier

Christophe Benech, Benjamin Clément, Michel Dabas, Lionel Darras, Lionel Flageul, Côme Parfant, Lola Perruchon-Monge, Cyril Schamper, Alain Tabbagh et Quentin Vitale, « Combined GPR and Electrostatic Prospection in the Roman Colony of Vienna (France) »ArcheoSciences, 45-1 | 2021, 27-30.

Référence électronique

Christophe Benech, Benjamin Clément, Michel Dabas, Lionel Darras, Lionel Flageul, Côme Parfant, Lola Perruchon-Monge, Cyril Schamper, Alain Tabbagh et Quentin Vitale, « Combined GPR and Electrostatic Prospection in the Roman Colony of Vienna (France) »ArcheoSciences [En ligne], 45-1 | 2021, mis en ligne le 16 août 2021, consulté le 29 mars 2023. URL : http://journals.openedition.org/archeosciences/8180 ; DOI : https://doi.org/10.4000/archeosciences.8180

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Auteurs

Christophe Benech

Corresponding author, Université de Lyon, CNRS, Archeorient, UMR 5133, Maison de l’Orient et de la Méditerranée, France

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Benjamin Clément

Université de Franche-Comté, CNRS, Chrono-Environemment, UMR 6249, Besançon, France

Michel Dabas

PSL University, CNRS, AOROC, UMR 8546, ENS, 75005 Paris, France

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Lionel Darras

Université de Lyon, CNRS, Archeorient, UMR 5133, Maison de l’Orient et de la Méditerranée, France

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Lionel Flageul

Sorbonne Université, UMR SU CNRS EPHE 7619 METIS, Paris, France

Côme Parfant

Université de Lyon, CNRS, Archeorient, UMR 5133, Maison de l’Orient et de la Méditerranée, France

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Lola Perruchon-Monge

Université de Lyon, CNRS, Archeorient, UMR 5133, Maison de l’Orient et de la Méditerranée, France

Cyril Schamper

Sorbonne Université, UMR SU CNRS EPHE 7619 METIS, Paris, France

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Alain Tabbagh

Sorbonne Université, UMR SU CNRS EPHE 7619 METIS, Paris, France

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Quentin Vitale

Éveha International, 161 avenue de Verdun, 94200 Ivry-sur-Seine, France, Université de Lyon, CNRS, Archeorient, UMR 5133, Maison de l’Orient et de la Méditerranée, France

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